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The historical historical evidence as aas a The evidenceagainst againstimplants implants major contributing factor to the buller steer syndrome is major contributing factor to the buller steer syndrome confounded by the fact that during the same time in is confounded by the fact that during the same time in whichthe thefeedlots feedlotswere werebeing beingmonitored monitoredand andan anincrease increase which in buller incidence was observed, the number of cattle on in buller incidence was observed, the number of cattle feed nearly doubled. This lead to an increase in the on feed nearly doubled. This lead to an increase in the number of animals per pen, and at the same time the number of animals per pen, and at the same time the dosage of anabolic agents fed or implanted to cattle dosage of anabolic agents fed or implanted to cattle increased substantially. increasedAlthough substantially. the use of growth promoting implants Although use steer of growth promoting implants plays a role in thethe buller syndrome, implants are not plays a role in the buller steer syndrome, implants entirely responsible for its occurrence, as bullers are are not entirelyeven responsible forwhere its occurrence, as bullers observed in feedlots implants are not usedare observed in feedlots where implants are not used (Irwin eteven al., 1979; Ulbrich, 1981). (Irwin etAlso, al., 1979; Ulbrich, 1981). although greater dosages of estrogenic Also, greater dosages of estrogenic implants mayalthough increase the possibility of bullers, greater implants may increase the possibility of bullers, greater dosages of implants also result in greater performance; dosages implants result in greater performance; reducingofthe implantalso dosage in order to reduce bulling in reducing the implant dosage in order to reduce a small percentage of cattle may also result in lostbulling inperformance a small percentage of weight cattle may result and carcass of thealso entire pen in lost performance and carcass weight of the entire pen resulting resulting in reduced profitability. in reduced profitability. The mounting behavior exhibited by steers Thefrom mounting behavior exhibited by steers suffering buller steer syndrome is often thought of suffering from buller steer syndrome is often thought as a sexual behavior, but typical sexual behaviors suchofas aslip-curling, a sexual behavior, but typical sexual behaviors such penile erections, and intromission are not asexhibited lip-curling, penileRiding erections, and intromission area not by riders. is therefore more likely way exhibited Riding is therefore more steer. likely a way for a steerbytoriders. exert dominance over another for a steer to mounting exert dominance over another The behavior seen amongsteer. feedlot buller The mounting behavior seen among feedlot buller steers is more likely to be related to social behavior, since steers more likely to be which relatedare to insocial behavior, in wildis species of ungulates the same since in wild species of ungulates which are in the same
taxonomic domestic beefbeef cattle, submissive taxonomicfamily familyas as domestic cattle, submissive behavior is expressed by allowing the dominant behavior is expressed by allowing the dominant animal animal to to mount. mount. One Klem et al. Oneobservational observationalstudy studybyby Klem et (1983) al. (1983) found that bullers were actually more aggressive than than found that bullers were actually more aggressive riders and the authors postulated that bullers may not be riders and the authors postulated that bullers may not be readily submitting to dominant riders. Social hierarchies readily submitting to dominant riders. Social hierarchies between cattle appear to play a role in the generation of between cattle appear to play a role in the generation of bullers in a feedlot setting. Dominant steers are naturally bullers in a feedlot Dominant arethey naturally more aggressive thansetting. other steers in thesteers pen, so like more aggressive than other steers in the pen, so they like to establish their dominance. Not surprisingly, when to establish their Notpenned surprisingly, steers first arrive at adominance. feedlot and are together,when the first arrive feedlot are together, the steers at a and penned number of bullers is at its highest. numberWhen of bullers is atare itsre-grouped, highest. the number of animals When animals are the number bullers rises again as new penre-grouped, members establish their of bullers rises again as new pen members establish social status. There is also evidence that suggests the their social status. Theredominance is also evidence that often suggests the expression of social occurs more in pens expression of socialofdominance occurs more often in pens with large numbers animals (Grognet, 2004; Brower with large numbers of animals (Grognet, 2004; Brower and Kiracofe, 1978; Irwin et al., 1979). and Kiracofe, 1978; Irwin et al., 1979). Hormonal blood levels have also been implied to Hormonal blood levels have also been be a factor that contributes to the occurrence of theimplied buller to besyndrome a factor in that to theEpp occurrence of the steer thecontributes feedlot industry. at al. (2008) buller steer syndrome in the tofeedlot Epp at reported that bullers, compared controlindustry. steers, have al. (2008) serum reported that bullers, compared to control suppressed concentrations of progesterone, steers, have suppressed serum concentrations increased estrogen and testosterone levels, and 74.5% of progesterone, estrogen andtype testosterone levels, greater levels ofincreased monoamine oxidase A (monoamine and 74.5% greater levelsresponsible of monoamine oxidase type A neurotransmitter enzyme for modifying (monoamine same neurotransmitter enzyme with responsible for behavior---the molecule associated modifying behavior---the same molecule psychopathic behaviors in humans) mRNAassociated activity. with psychopathic behaviors in humans) mRNA activity. 15
